PMID:4124306
| Citation |
Campbell, JH, Lengyel, JA and Langridge, J (1973) Evolution of a second gene for beta-galactosidase in Escherichia coli. Proc. Natl. Acad. Sci. U.S.A. 70:1841-5 |
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| Abstract |
Mutants of E. coli K12 with deletions of the beta-galactosidase gene (lacZ) can reacquire the ability to hydrolyze beta-galactosides during prolonged intense selection for growth on lactose. Full lactose competence is restored through a sequence of at least five mutations. Cell extracts of these derived strains hydrolyze o-nitrophenyl-beta-D-galactoside, the standard substrate for assay of beta-galactosidase. The enzyme responsible for this activity differs in its immunological, kinetic, and sedimentation characteristics from the lacZ beta-galactosidase of wild-type E. coli. Its genetic determinant, designated ebg-5, maps at 59 min on the E. coli chromosome, whereas the lac operon maps at 10 min. We suggest that a gene not involved in lactose utilization has been progressively changed into a form capable of specifying a beta-galactosidase and that this process is similar to that whereby genes with new functions are evolved by natural selection. |
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| Keywords |
Centrifugation, Density Gradient; Chromosome Mapping; Epitopes; Escherichia coli/enzymology; Escherichia coli/metabolism; Galactosidases/biosynthesis; Galactosidases/isolation & purification; Genes; Lactose/metabolism; Mutation; Transduction, Genetic |
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